Public domain data

These data have no specific confidentiality restrictions for users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.

The recommended acknowledgment is

"This study uses data from the data source/organisation/programme, provided by the British Oceanographic Data Centre and funded by the funding body."

Neil Brown MK3 CTD

The Neil Brown MK3 conductivity-temperature-depth (CTD) profiler consists of an integral unit containing pressure, temperature and conductivity sensors with an optional dissolved oxygen sensor in a pressure-hardened casing. The most widely used variant in the 1980s and 1990s was the MK3B. An upgrade to this, the MK3C, was developed to meet the requirements of the WOCE project.

The MK3C includes a low hysteresis, titanium strain gauge pressure transducer. The transducer temperature is measured separately, allowing correction for the effects of temperature on pressure measurements. The MK3C conductivity cell features a free flow, internal field design that eliminates ducted pumping and is not affected by external metallic objects such as guard cages and external sensors.

Additional optional sensors include pH and a pressure-temperature fluorometer. The instrument is no longer in production, but is supported (repair and calibration) by General Oceanics.

Instrumentation and Protocols

The instrument used was a Neil Brown Instrument Systems CTD which measured pressure, temperature and conductivity. Up to 12 water bottles were put on the wire during the CTD lowering, to provide calibration values and some back-up station data. The output was recorded on magnetic tape and values logged by hand at 100db intervals. Lowering and retrieval rates of 0.5 to 1.5 m/s were employed and the sensors were flushed with distilled water on recovery. The sea water samples were analysed using a Guildline Autolab Salinometer. Reversing thermometers were calibrated before and after the cruise.

Calibration

Pressure

In-situ calibration was possible by comparison between the CTD and the pressure determined from pairs of reversing thermometers (protected and unprotected).

Temperature

In-situ calibration was possible by comparing of the CTD temperatures and reversing thermometers separating the deep and shallow measurements.

Salinity

The salinity data were calibrated using one set of calibration constants for the entire leg of the cruise. These were determined from 10 water samples on each station.

Data Processing

Original values were averaged over an interval of one second and calibration coefficients and correction factors applied. A time constant correction algorithm was employed to compensate for the slower response of the platinum resistance thermometer. Differences between successive values of each parameter were examined; the mean difference and its standard deviation calculated and values greater than several standard deviations from the mean difference were checked. Genuinely suspect data were then replaced by interpolated values. Derived quantities were computed from algorithms published by Fofonoff et al (1974). The data have been averaged to give 1 value approximately every decibar.